The present invention relates to a method for riveting, or self-piercing, and a device for carrying out the method. The large forces on a workpiece which occur when a rivet is set or during piercing must be compensated by a counterforce. This is usually achieved by supporting the workpiece on a counterforce structure, which preferably substantially has the shape of a C and is therefore also usually designated as a C-bracket.
For the precise setting of a rivet or accurate self-piercing it is important to know how deeply a rivet or a die has penetrated into the workpiece. This problem arises in particular when large workpieces are being processed, where the counterforce structure (C-bracket) is very large. In practice arm lengths of C-brackets occur of up to 1.5 metres. Deformation of the counterforce structure occurs in particular with large forces acting on the workpiece, so the actual self-piercing depth or the rivet head projection is determined only inaccurately. This problem is particularly significant when short rivets, hard materials and large workpieces are used. Distortion of the counterforce structure results in considerable inaccuracies with respect to the piercing depth or the rivet head projection.
To date it has been usual to construct the counterforce structure as large and as resistant to bending as possible. To keep deformation within an acceptable scope considerable expenditure and costs in the construction of the counterforce brackets have been necessary. Compensation of any deformations of the counterforce bracket took place manually, after the fault had been detected empirically.